Angle insensitive color filters have significant application prospects in the fields of liquid crystal display, color printing, sensor detecting, anti-counterfeiting and so forth. The traditional chemical dye color filters achieve the filtering effect as the result of a wavelength-selective absorption of the particular functional groups. However, dyes will cause a material instability and a significant environmental burden. The optical thin film filters by multi-layer interference performs well with a high peak transmittance, a tailored bandwidth, and stable specifications. However, they present an obvious blue-shift phenomenon, that is, spectral curves will move to short wavelengths with an increasing angle of incidence, which limits the application at large incidence angles. In recent years, a variety of color filters based on sub-wavelength structures have been proposed owing to the intensive research on the electromagnetic theory of subwavelength grating and the development of micro/nano fabricating techniques. The guided mode resonance light filters are able to switch the energy of the incident light between reflection and transmission in a very small range via the coupling between the high-order leaky mode and the waveguide mode in the media of grating, so as to obtain the filters with ultra-narrow band. However, the guided mode resonance filters are very sensitive to the incidence angle. Even though the incident angular tolerance can be improved via structure optimization and other means, it is still very difficult to get higher insensitivity of the incidence angle. By fabricating one-dimensional subwavelength grating of silicon on the quartz substrates, Kanamori et al obtained transmission color filters in the three colors of red, green and blue. But their properties will change with the incidence angle (Fabrication of transmission color filters using silicon subwavelength gratings on quartz substrates, IEEE Photon. Technol. Lett. 18, 2126-2128 (2006)). In addition, researchers also proposed stacked subwavelength grating structure to obtain the color filters with better performance at normal incidence by stacking two layers of one-dimensional or two-dimensional subwavelength gratings. To improve the insensitivity of the incidence angle, Cheong et al proposed the use of silicon with high refractive index as the material of two-dimensional subwavelength grating to realize intense modulated grating and obtain high angular tolerant reflective filters (High angular tolerant color filter using subwavelength grating, Appl. Phys. Lett. 94, 213104-3 (2009)). However, their properties deteriorate at different azimuth angles and are not suitable for practical application. Besides, the electron beam lithography technique is used in the manufacturing process. It is high cost, time-consuming, and difficult to manufacture.
Among the nano-material structures, orderly porous structure periodically arranged is widely studied and applied in numerous research fields. Porous alumina, with pores regularly hexagonally latticed, has attracted more and more researchers to study into thoroughly and widely due to its simple and convenient manufacturing methods. At present, the study of porous alumina concentrates mainly focuses on the material characteristics and the application of the physical structure of the material, such as the producing of the nanotube, the transfer of the porous structure, the observation of quantum dot structure, and so forth.
Atomic layer deposition (ALD) technology is a method of forming a film by alternately feeding gas precursor pulse into the reactor to absorb and have chemical reaction on the deposition substrate. It was proposed by a scientist from Finland in 1970s. With development of the microelectronics and deep submicron chip technology in the middle of 1990s, ALD has been extensively applied in the field of semiconductor. Due to the self-confinement of ALD surface reaction, theoretically, the deposition accuracy of ALD can reach atomic level. Furthermore, compared with the traditional deposition method for an optical film, the film by ALD has incomparable advantages in term of deposition temperature, aggregation density and conformality. So the use of ALD in the preparation of optical films gradually becomes a hot topic in research.
Although research and application based on the combination of porous alumina and atomic layer deposition has been proposed constantly, as far as we know, the research on the manufacturing of incident angle insensitive color filters by using atomic layer deposition to fill the porous alumina with the high refractive index oxides as the template has never been proposed. The manufacturing of incident angle insensitive color filters in the present invention is simple and of low cost. Therefore, the present invention is expected to be extensively applied in the fields of liquid crystal display, color printing, sensor detecting and anti-counterfeiting and so forth.